Radiant energy scanner



Aug. 7, 1962 R. M. ASHBY RADIANT ENERGY SCANNER 5 Sheets-Sheet 1 FiledAug. 29, 1956 90E on i a m m 9 4 MN q mm mm mmxwi o mommw A mmtim mmEimmmsi A $5:

m m N w IN VEN TOR.

ROBERT M. ASHBY AT TO RN EY Aug. 7, 1962 R. M. ASHBY RADIANT ENERGYSCANNER 3 Sheets-Sheet 2 Filed Aug. 29, 1956 INVEN TOR. ROBERT M. ASHBYQQ XWW ATTORNEY 1962 R. M. ASHBY 3,048,844

RADIANT ENERGY SCANNER Filed Aug. 29, 1956 3 Sheets-Sheet s FEED HORN l9(a) RELATIVE PHASE FEED HORN 2o FEED HORN l9 (b) RELATIVE AMPLITUDE FEEDHORN 2o I (D)BEAMPOSITION:I: 4 gi; 1:; I,

I I Ki l ROTATION 0F PHASE SHIFTER INVENTOR.

ROBE RT M. ASHBY ATTORNEY United States atent Qfltice 3,048,844 RADIANTENERGY SCANNER Robert M. Ashby, Pasadena, Calif., assignor to NorthAmerican Aviation, Inc. Filed Aug. 29, 1956, Ser. No. 606,909 16 Claims.(Cl. 343-777) This invention relates to a radiant energy scanner, andmore particularly it relates to the microwave portion of a conical radarscanner.

In a radiant energy scanning device, it is desirable to provide aminimum of equipment and a minimum of mechanical motion. In mostscanning systems particular care must be taken to dynamically balancethe mechanical elements to avoid the undesired effects of vibrations onthe scanning system and other associated equipment. An early type ofconical scanning was provided by a device in which the microwave portionwas displaced slightly from the focal point of the reflector, causingthe lobe of the transmitted energy to likewise be displaced from theaxis of the reflector. The microwave feed portion then was rotated andthe lobe thus caused to move in a conical scan. Such a device was notbalanced mechanically. Also, it did not make full use of the reflectingcapabilities of the reflector. This invention provides conical scanningwithout the rotation of the reflector or the microwave feed portion.Conical scanning is obtained by varying the illumination of themicrowave feed apertures. This variation of aperture illumination isaccomplished by the rotation of the polarization of electromagneticwaves within a resolver. The antenna feed does not rotate and it may beplaced substantially at the focal point of the reflector.

In one embodiment of the invention the conical scanner is adapted totransmit the lobe directly on the reflector axis as may be desired formonopulse type operation in which control scanning is not used.

By the theorem of reciprocity the device may scan in conical fashion soas to receive any radiant energy as well as to transmit it. Scanning, asused herein, therefore, includes both reception and transmission.

It is, therefore, an object of this invention to provide an improvedconical scanning device.

It is another object of this invention to provide a radiant energyscanner having a minimum of rotating equipment.

It is still another object of this invention to provide a conicalscanner utilizing waves of rotating polarization.

It is another object of this invention to provide a conical scannerwhich may be readily adjusted for monopulse operation.

A further object of this invention is to provide an antenna wave-guidesection producing a circularly polarized wave.

Still another object of this invention is to provide an antennawave-guide section producing a rotating linearly polarized wave.

Other objects of invention will become apparent from the followingdescription taken in connection with the accompanying drawings, in whichFIG. 1 is a block diagram of the device of the invention;

FIG. 2 is an illustration of one phase shifter portion of the device ofthe invention;

FIG. 3 is an illustration of the device of the invention partially incross section;

FIG. 4 is a diagram of phase, amplitude and beam position;

FIG. 5 is an illustration of the rotatable phase shifter of theinvention showing another position of the phase shifter;

FIG. 6 is a front view of a reflector;

And FIG. 7 is a cut-away end view of waveguide 8 illustrating orthogonaltakeoifs.

In FIG. 1, an antenna feed 1 is shown illuminating a reflector 2. In thetransmission mode, the signals transmitted by antenna feed 1 arereceived from range duplexer 3 through A phase shifter 4, and A 90rotating phase shifter 5, and a A 90 phase shifter 6. In the energyreception mode, antenna feed 1 provides signals to phase shifter 6,phase shifter 5, phase shifter 4, and range duplexer 3, and azimuth andelevation error duplexer 7.

FIG. 2 is an illustration of A 90 fixed phase shifter 4 of FIG. 1. Alinearly polarized wave enters waveguide section '8 at the neareropening 9, and is illustrated as vector A. A fixed dielectric slab 10resolves this vector into its two components, the vectors A, and A,,.One lies normal to the dielectric slab, the other is parallel to theplane of the slab. The slab is chosen so that its length and dielectricconstant produce a 90 time phase lag in the component A, which isparallel to the plane of the slab. The A 90 phase shifter is a fixeddielectric slab 10 or a metallic slab of suitable dimensions to causethe vector A; to be delayed 90 along the length of waveguide 8 behindthe vector A This results in a circularly polarized wave at the outputend 11 of Waveguide 8. It will be noted that the phase shifter slab isat a 45 angle with the input linear vector A. The time phaserelationship of the vectors A, and A, at the output end are alsoillustrated. Explanation and clarification of the concept illustrated inFIG. 2 may be obtained from Hyper and Ultra High Frequency Engineering,by Sarbacher and Edson, pp. 101 et seq.

Referring now to FIG. 3, illustrating the conical scanner, it can beseen that the A 90 fixed phase shift is accomplished by metal fins 12and 13 which have the same effect as the dielectric slab 10 of FIG. 2.Subsequent to this phase shifter are illustrated two rotating A 45 phaseshifters 14 and 15, rotated by motor 16. In conical scan, phase shifters14 and 15 are maintained in alignment and therefore form a rotating A 90phase shifter. As the outgoing wave is received in waveguide 23, it ispassed through duplexer 3 and section 21 to section 4 of the Waveguide.Up to this point, the outgoing wave is linearly polarized. At it passesthrough section 4 it becomes circularly polarized, as explained inreference to FIG. 2. As the wave leaves section 5, due to the tworotating 45 phase shifters, the wave is rotating and linearly polarized.Waveguide 17 and waveguide 18 take ofl? from phase shifter 5 at rightangles with respect to each other. FIG. 7 illustrates the similarorthogonal takeoff apertures 35 and 36 of waveguides 21 and 24. Theorthogonal takeoff apertures of waveguides 17 and 18'are similarlylocated. The rotating linearly polarized wave is extracted through twoorthogonal waveguide takeofis 17 and 18 which guide the energy tofeedhorns 19 and 20. The apertures of the two feed horns are locatednear the focus of the paralbolodial reflector. The one horn 19 is aboveand to the right of the reflector axis, while the other horn 20 is belowand to the left of the reflector axis.

Such disposition is termed herein as being :laterally and' verticallyspaced apart. An additional 90 phase shift section 6 is inserted in thewaveguide leading to horn 20; or alternately, the length of thewaveguide to feedhorn 20 may be made correspondingly longer to cause a90 phase shift in the relative outputs of feedhorns 19 and 20. Assubsequently explained herein, the transmitted lobe 33 rotates aboutcentral axis 34 as illustrated to provide conical scan.

FIG. 4 shows the phase, amplitude and beam position of the radiofrequency fields at the apertures of feedhorns 19 and 20 as a functionof the rotating phase shifter. Due to the relative geometry of thewaveguide takeoffs 17 and 18, as the phase shifter 5 rotates, there is aphase shift of 180 between the waves extracted at takeoffs 17 and 18.This is due to the inherent coupling geometry that two orthogonaltakeoffs present to the rotating linear polarization. At zero radiansrotation, FIG. 4a, the 90 phase lag in the waveguide takeoif 18establishes a relative 90 phase lead in the wave that is radiated fromhorn 19 with respect to the wave radiated from horn 20. However, forpositions of the phase shifter between and 1r there is a shift to 90phase lag. It is observed, FIG. 4b, that the amplitude of the radiofrequency wave at horn 20 follows a sine wave distribution as a functionof the rotation angle; whereas the amplitude of the radio frequency atfeedhorn 19 follows a cosine distribution. This amplitude modulation ofthe energy being fed into the horns is caused by the resolver-likeaction of the cylindrical section of the waveguide and the twoorthogonal takeoifs during this mode of operation. there is the positionof the rotating A 90 phase shifter 5 (the two A 45 phase shifters) forwhich the linear polarization incident upon the orthogonal takeoffs 17and 18 will be aligned with the waveguide takeoff 17 which feeds horn19. At this position, there will be a maximum of energy coupled into thehorn 19, while there is no energy coupled into the horn 20, because thewaveguide takeofi feeding horn is at right angles to the linearlypolarized Wave. Let this position of the phase shifter, the zeroposition in FIG. 4, be considered as the reference. By rotating the A 90phase shifter the polarization of the transmitted wave is rotated so asto couple equally into both waveguide takeofls. At this point, bothhorns will receive waves of equal amplitude. An additional rotation ofthe A 90 phase shifter will bring the linearly polarized transmittedwave in the cylindrical section into alignment with the waveguidetakeofl feeding born 20. At this point, a maximum power is radiated fromhorn 20 whereas no power is radiated from horn 19. As the A 90 phaseshifter is rotated still further, the energy is transferred again fromhorn 20 to 19 in a sinusoidal manner.

FIG. 4c also shows the orientation of the beam in space for this type ofexcitation. When there is no energy being radiated from horn 20, thetransmitted beam is essentially down, as shown in FIG. 4. This is causedby the fact that horn 19 is located above the axis and the radiationtherefrom, upon striking the reflector, is transmitted outwardly belowthe axis. The distances horns 19 and 20 are laterally displaced from thefocal point of the reflector introduce errors which may be minimized asexplained later with reference to FIG. 6. The deflection of the conicalbeam in azimuth is obtained because the excitation of the feedhorns areout of phase which was mentioned previously. When the phase shifter isrotated to the position equal energy is radiated from both horns 19 and20, but they are out of phase and the transmitted beam is radiated tothe left of the antenna axis. As the phase shifter rotates to positionall of the radiated energy appears to come from the horn 20 which islocated below the axis of the reflector; therefore, the beam isreflected upwardly and appears above the antenna axis. When the phaseshifter is located at %1r, the radiated beam is to the right of theantenna axis, and when the phase shifter reaches the point 1r, the beamis again in the down position. It should be observed from FIG. 4 thatthe antenna conical scan rate is twice the rotation rate of the phaseshifter 5.

During reception, the antenna pattern, by the theorem of reciprocity, isthe same as for transmission so that the For example,

reflected energy returns by the same path through the waveguides and thephase shifters where it is coupled in the normal manner to aconventional receiver designed to operate with a conical scanningsystem.

FIG. 5 illustrates how the device of the invention is used in the moreconventional monopulse scanning if desired. This is done by simplyrotating the two A 45 slabs 14 and 15 so that they are oriented at rightangles to each other. Eflectively then, they cancel each other. They mayeither be held stationary or rotated in this relative relation.

In the monopulse transmission, the circularly polarized wave is receivedat the orthogonal takeofls 17 and 18, FIG. 3, and equal energy iscoupled into both horns 19 and 20. However, there is an inherent timephase lag of the wave in horn 19 relative to the wave in horn 20 that isassociated with the circularly polarized wave within the cylindricalsection. This lag is cancelled by the phase shift section 6 in feedhorn20. Since the tw horns are then radiating equal energy in time phase,the transmitted beam appears directly on the axis as is desired formonopulse operation.

In monopulse reception, the antenna radiation pattern associated withthe range receiver is the same as the transmission pattern. Because ofthe vertical offset of horns 19 and 20, the energy reflected from atarget off axis in elevation will excite the horns 19 and 20 essentiallyin time phase but with unequal amplitudes. Due to the waveguide betweenhorn 20 and takeoff 18 being longer than between horn 19 and takeoif 17,these waves are in quadrature upon arrival at the circular portion ofthe waveguide. Since the waves are not equal in amplitude, they excitean elliptically polarized wave in the round guide. This ellipticallypolarized wave may be thought of as being composed of two circularlypolarized waves of opposite sense and of unequal magnitude. As thesecircularly polarized waves pass the fixed phase shifter in section 4,they are transformed into two linearly polarized components in spacequadrature. One of these components is coupled into waveguide takeoff 21and provides range information to duplexer 3. Duplexer 3, in turn,passes the signal t an output waveguide 22 which is connected to therange receiver of the device. The other linearly polarized componentcouples into waveguide takeolf 24 and corresponds to the elevation errorsignal. If the target is off axis in azimuth, the two feedhorns 19 and20 are excited by waves of approximately equal amplitude but differentin phase. At the circular portion 8 of the Waveguide, the waves fromhorns 19 and 20 result in excitation of the two essentially equalamplitude components at right angles in the round guide but with timephase differing up to 90, depending upon the azimuth error angle. Thecomposite wave in the round guide may be resolved again into twocomponents which couple into waveguide takeoifs 21 and 24. That portioncoupling into output waveguide 21 is, again, the range reference. Theenergy in waveguide takeoff 24 contains the azimuth error informationand is in time phase quadrature with the elevation error informationcontained within the same channel. These azimuth and the elevation errorsignals are propagated in waveguide takeoff 24 and pass through:duplexer 7 and out waveguide 25 to the error receiver of the device.After detection and intermediate frequency amplification, the azimuthand elevation error signals are then separated in a quadrature errordetector (not shown). As with other systems, the relative phase of thesignal in the sum channel, waveguide 22, may be used to determinewhether the signal in the error channel comes from a target above orbelow the antenna axis or to the left or to the right in azimuth.

A practical reflector may be a paraboloid or an elliptical paraboloid.The previous discussion indicated that the azimuth error informationresulted from the phase difference in the excitation of horns 19 and 20.To eliminate the off axis in azimuth amplitude variations in the horns19 and 20 excitation, the two halves of the reflector are separated, asshown in FIG. 6, to result in the center of phase of each hornsradiation lying along the vertical line containing the half paraboloidvertex. The two half paraboloids are then joined in region 32 by aparabolic cylinder.

A signal off axis in elevation results in a small amount of time phasedifference in the signals excited in the horns 19 and 20. There is noway of eliminating the resulting azimuth channel cross-couplingcomponent. Therefore, the distance 32 is made slighty wider or narrowerthan the distance between feedhorns 1'9 and 26 in FIG. 6 so as to resultin an amount of azimuth to elevation channel crosscoupling of amagnitude and direction to compensate for the elevation to azimuthchannel cross-coupling.

A compact conical scanner, readily adaptable to monopulse operation, isthus obtained with no externally moving parts.

Although the invention has been described and illustrated in detail, itis to be clearly understood that the same is by way of illustration andexample only and is not to be taken by way of limitation, the spirit andscope of this invention being limited only by the terms of the appendedclaims.

I claim:

1. A conical scanning device comprising means for resolving anelectromagnetic wave to feed two signal channels comprised of twowaveguides terminating in two laterally and vertically displacedfeedhorns, with electromagnetic waves of sinusoidally-varying amplitudesand a relative time phase difference of 90, and means for reversing therelative phase in said channels between lead and lag every 90 of saidsinusoidally-varying waves.

2. A conical scanning device comprising means providing anelectromagnetic wave, a pair of signal channels comprised of twowaveguides, means for coupling said electromagnetic wave into saidwaveguides with sinusoidally-varying amplitudes and a relative timephase difference of 90, the relative phase in said channels reversingbetween lead and lag every 90 of said sinusoidally-varying waves, a pairof feedhorns located laterally and vertically apart, each of saidfeedhorns connected to a respective waveguide.

3. A conical scanning device comprising means providing anelectromagnetic wave, a pair of waveguides, means for coupling twocomponents of said electromagnetic wave into said Waveguides withsinusoidally-varying amplitudes, said components being displaced in timephase with respect to each other, and a pair of feedhorns locatedlaterally and vertically apart, each of said feedhorns connected to arespective waveguide, reflector means cooperatively associated with saidfeedhorns.

4. A waveguide, a rotatable 90 phase shifter located within a section ofsaid waveguide, said waveguide comprised of two 45 phase shiftingsections, means for displacing each of said 45 phase shifting sectionsrelative to the other and means for rotating said phase shifter.

5. In a radiant energy scanner, a waveguide, means providing acircularly polarized wave to said waveguide, a rotatable 90 phaseshifter adapted for continuous rotation, said phase shifter beinglocated in said waveguide, and two waveguide takeoffs located withrespect to each other so as to receive orthogonal components of theoutput wave from said phase shifter and antenna feed means connected toreceive the output provided by both said takeotfs.

6. In a radiant energy scanner, a waveguide, means providing acircularly polarized wave to said waveguide, a rotatable 90 phaseshifter adapted for continuous rotation, said phase shifter beinglocated in said waveguide, and two waveguide takeofis locatedorthogonally with respect to each other so as to receive orthogonalcomponents of the output wave from said phase shifter and antenna feedmeans connected to receive the output provided by both said waveguidetakeoffs.

7. The combination recited in claim 6 wherein said antenna feed meansincludes a first antenna feed connected 6 to receive the output providedby one of said waveguide takeoffs, and a second antenna feed connectedto receive the output provided by the other of said waveguide takeolfs,and a phase shifter located in one of said antenna feeds.

8. In a radiant energy scanner, a waveguide for receiving a linearlypolarized wave, a fixed 90 phase shifter located in said waveguide andoriented at 45 with respect to said linearly polarized wave, a rotatably90 phase shifter located in said waveguide, two waveguide takeolfsorthogonally located with respect to each other so as to receiveorthogonal components of the output of said waveguide, and antenna feedmeans comprising two channels connected to receive respective orthogonalcomponent outputs of said waveguide.

9. In a radiant energy scanner, a waveguide for receiving a linearlypolarized wave, a fixed 90 phase shifter located in said waveguide andoriented at 45 with respect to said linearly polarized wave, a rotatable90 phase shifter located in said waveguide, two waveguide takeolfsorthogonally located with respect to each other and connected to receivethe outputs of said rotatable 90 phase shifter, a first feedhornconnected to receive the output of one of said takeoifs, a secondfeedhorn connected to receive the output of the other of said takeoffs,a reflector, said feedhorns being located laterally and vertically apartsubstantially at the focal point of said reflector.

10. The combination recited in claim 9 wherein is included a 90 phaseshifter between one of said takeoffs and the feedhorn connected toreceive its output.

11. In a radiant energy scanner, a Waveguide for receiving a linearlypolarized wave, a fixed 90 phase shifter in said waveguide located at 45with respect to said linearly polarized wave, a rotating 90 phaseshifter located in said wave guide, first and second takeoffs connectedat one end of said waveguide, said takeofis located orthogonally withrespect to each other, third and fourth waveguide takeoffs connected atthe other end of said waveguide, said third and fourth takeoffs locatedorthogonally with respect to each other, and first and second antennafeed means connected to receive the outputs provided by said first andsecond takeofis, respectively.

12. The combination recited in claim 11 wherein said rotating 90 phaseshifter comprises a plurality of sections adapted to be rotated withrespect to each other.

13. The combination recited in claim 11 wherein said rotating 90 phaseshifter comprises two 45 phase shifters adapted to rotate in alignmentand further adapted to be rotated in a position in which said shiftersare located at right angles with respect to each other.

14. In a radiant energy scanner, a waveguide for receiv ing a linearlypolarized wave, a fixed 90 phase shifter in said waveguide located at 45with respect to said linearly polarized wave, a rotating 90 phaseshifter located in said waveguide, first and second takeoffs connectedat one end of said waveguide, said takeoffs located orthogonally withrespect to each other, third and fourth waveguide takeoifs connected atthe other end of said waveguide, said third and fourth takeoifs locatedorthogonally with respect to each other, first and second antennafeedhorns connected to receive the outputs of said first and secondtakeoifs, a 90 phase shifter connected between the output provided byone of said takeoffs and one of said feedhorns, a reflector, saidfeedhorns being disposed laterally and vertically apart substantially atthe focal point of said reflector.

15. In a radiant energy scanner, a waveguide for receiving a linearlypolarized wave, a fixed 90 phase shifter in said waveguide located at 45with respect to said linearly polarized wave, a rotating 90 phaseshifter located in said waveguide, first and second takeoifs connectedat one end of said waveguide, said takeoffs located orthogonally withrespect to each other, third and fourth waveguide takeoffs connected atthe other end f i N p a wave from said phase shifter, antenna feed meanscon- 10 nected to receive the output provided by both said waveguidetakeofis, said antenna feed means including a first antenna feedconnected to receive the output of one of said waveguide takeoffs, and asecond antenna feed connected to receive the output of the other of saidwaveguide takeoifs, and a 90 phase shifter located in one of saidantenna feeds, said antenna feeds comprising feedhorns located laterallyand vertically apart.

References Cited in the file of this patent UNITED STATES PATENTS2,438,119 Fox Mar. 23, 1948 FOREIGN PATENTS 1,102,590 France May 11,1955 OTHER REFERENCES Electronics, June 1952, pages 156, 158, 162, 166.

